Polythiocyanuric acid-functionalized MoS2 nanosheet-based high flux membranes for removal of toxic heavy metal ions and congo red

Abstract

MoS2 nanosheets were functionalised by polythiocyanuric acid (PTCA) in varying ratios (MoS2:PTCA = 1:1, 1:2, 1:3). The modification enabled the materials to be strongly adsorbed onto polyethersulfone (PES) membranes without requiring prior exfoliation. This was in strong contrast to MoS2 itself. Spectroscopic characterisation indicated adhesion was through strong hydrophobic π-π* stacking and electrostatic interactions between PTCA and PES. Modification of the PES resulted in an increased hydrophilic character, as evidenced by a decreasing contact angle (78° unmodified, 40° – 50° modified) and an increase in water uptake (WU) from 12.8% to 17 – 27% (%WU = [(Ww / Wd) – 1] × 100%, where Ww and Wd refer to wet and dry membrane weights, respectively). When modifying PES using different MoS2-PTCA ratios, increasing the PTCA content decreased the permeate flux and pure water flux, while increasing the % removal of congo red, Hg(II), Cr(VI) and Pb(II) to approximately 80%. The potency of the membranes is ascribed to the formation of lamellar structures with increased hydrophilicity and the synergy between the disulfide linkage and absorptive capabilities of the MoS2.